A simple wind tunnel built by simple men to design a simple plane
I design wind tunnels among other things. That’s my job. It’s a fun job and I get to travel all over working on wind tunnels and all sorts of facilities. Because of this, I have a deep appreciation for historic wind tunnels. Like the one above.
The wind tunnel pictured above was designed and built by the Wright Brothers. It has a maximum wind speed of about 35 mph, which was plenty for them. It allowed them to test models of their Wright Flyer before sticking Wilbur in the real thing and putting his butt on the line.
Since then, wind tunnels have grown, become more specialized, and have become much more technologically advanced. There are climatic wind tunnels, low speed aerodynamic wind tunnels, transonic wind tunnels, supersonic and hypersonic wind tunnels. They are used for testing everything from automobiles to aircraft to spacecraft to skiers.
The main fan at the GM Aerodynamic wind tunnel in Warren, MI
A wind tunnel is a fairly simple device. In a closed-loop tunnel, a fan blows air around a circuit. A contraction just before the test section speeds up the wind using a venturi effect. Usually there is a large settling chamber just ahead of this contraction where the wind speed is near zero. Using Bernoulli’s equation, the wind speed is calculated using the settling chamber static pressure (which is the total pressure since air speed if minimal) and the static pressure in the nozzle. Transonic, supersonic and hypersonic wind tunnels will used compressed air or even compressed, supercooled nitrogen to simulate or replicate the Mach numbers required.
Aerodynamic wind tunnels are some of the simplest, but also the most precise. The aerodynamics on a vehicle, aircraft or spacecraft can be affected by the test section walls. Therefore, the test sections are usually very large to move the walls as far away from the vehicle as possible. Other systems like slotted walls can negate this effect by creating a suction along the walls that tricks the air into behaving as if a wall is not there. Many newer aerodynamic tunnels are also being used for acoustic research and have acoustic treatments in them to deaden the amount of sound transmitted by the facility so that only the sound transmitted from the vehicle is measured. More recently, rolling road systems are being used to simulate the aerodynamic effects of a the road under the vehicle.
BMW's aerodynamic wind tunnel with a rolling road
Climatic wind tunnels, on the other hand, can be temperature controlled, humidity controlled, have full solar simulation system (using lights and filters to simulate the spectrum and heat of the sun), and even snow and rain simulation. For these tunnels, huge refrigeration, steam and other systems are used to get the capabilities required.
The National Transonic Facility at NASA's Langley Research Center
The purpose of wind tunnels is to collect data. The data acquisition systems can be simple, off-the-shelf type systems or more complex, high-speed systems. One of the most impressive is the system at the National Full-Scale Aerodynamic Complex (NFAC) at NASA’s Ames Research Center (hell, that entire facility is impressive). It can measure almost 1,000 channels at up to 80 MB/sec. It is one of the fastest data acquisition systems in existence.
The nice thing about wind tunnels is they are based on physics. Physics doesn’t change. There are still ways to innovate, but the same concept that the Wright Brothers used on their wind tunnel in 1903 is the same concept that we are using on the design of wind tunnels today.
[Image Credits: National Museum of the Air Force, General Motors, bimmertoday.de, NASA]
You know, there are dyno shops all over the place who, for
your firstborn childa modest fee will allow you to test your car and see what your horsepower numbers are at the wheel. I can't help but wonder how long it's going to take before shops start creating their own wind-tunnels so that people can test to see how much of an improvement is provided by their ridiculous body kits, park-bench rear spoilers and fart-can exhausts.Maybe if shops would start doing that, we could end that awful trend once and for all.
Probably not.
I think the big hinderance for that right now is the cost of a balance and a wind tunnel designed for aerodynamics. The BMW tunnel pictured above was on the order of $10 million. The balance itself is several million dollars. Part of the reason is the precision, plus the fact that there are only like 2 companies that make these.
You can buy time in existing wind tunnels. It isn't cheap, but race teams use the Lockheed wind tunnel in Georgia, Windshear Inc's new wind tunnel in Concord (designed, built and operated by my company), Swift's wind tunnel in California, and others. For the demand vs. cost, it's usually cheaper to buy time in someone else's facility than to build your own.
"They are used for testing everything from automobiles to aircraft to spacecraft to skiers."
And, apparently, James May.
<img src="http://img.youtube.com/vi/hmYC9zBseSw/0.jpg" width="400">
Can't see it, but his hair must be demonstrating a slight Kamm effect, giving his face unnaturally low drag.
[youtube e6reT9Ux_gI http://www.youtube.com/watch?v=e6reT9Ux_gI youtube]
I love wind tunnels
Fun times post!
Ok, Mr Engineerd, what would be the best way to go about building one's own home wind tunnel to test things on? How this would be useful is dubious but fun it would be. As for scale, my first thought would be standard model car size scale but really probably the scale of what ever is easiest to build.
http://static.rcgroups.net/forums/attachments/1/7… is a drawing of a 10 meter wind tunnel based on Notre Dame University's tunnel. I have a few other links to other efforts I can post later if anyone is interested. Happy new year , Mike
… track backe bei http://www.bloghotel.org/nellieildefonso/ ……
bon , votre blog modèle est vraiment bon , je suis recherche pour un nouveau thème pour mon moncler doudoune propre personnel site Web , j’aime vôtre, maintenant je vais aller recherche le similaires design !…